Large messaging solutions are typically deployed across multiple machines, creating a distributed solution. The storage component of a solution often times requires a replication solution to protect against outages and/or data loss due to failures within the system.
Asynchronous log shipping has been used to provide an effective replication solution at a relatively low cost. However, asynchronous log shipping can experience data loss in the event of failure. This is because the asynchronous nature of the solution does not guarantee that all changes performed by an active data copy are immediately replicated to other servers. Users are thus forced to make a tradeoff between these recovery characteristics versus costs and complexity.
An email deployment can employ redundant frontend and backend servers, where mailbox storage is provided by the backend servers. The frontend servers can provide protocol services (e.g., POP and IMAP) and also client access services (e.g., browser-based mail reading and mobile device mail synchronization).
The backend servers can employ asynchronous log shipping to replicate the mail database between the configured copies and use an active/passive mechanism to manage changes to both copies. However, a log shipping solution can result in some amount of user data being lost if a server crash causes a failover.